In recent years, the demand for high-speed operation has increased for the spindle for machine tools with the aim of improving the cutting efficiency. In addition, in recent years, in order to improve the efficiency of production, corresponding needs to 5-axis working machine capable of machining a complex shaped workpiece without a changeover, without using a plurality of machine tools have emerged. In the 5-axis working machine, because the spindle and the table turn, from the demands for the space saving due to shortening of the turning radius, or power saving due to the reduction in inertia at the time of turning, the reduction in weight and the like, reduction in the axial length of the spindle is required.
Grease lubrication, oil-air lubrication, oil mist lubrication, and the like can be cited as lubricating methods that are widely adopted for machine tool spindles. Generally, oil-air lubrication is adopted in the region of high-speed rotation (dmn 1,000,000 or more). As a conventional oil-air lubrication, there is known a system for supplying a high-pressure air and fine oil particles to the interior of the bearing from the side surface of the bearing, using a lubricating oil nozzle piece 101 disposed on the side of the bearing 100 illustrated in FIG. 8A, or a lubricating oil nozzle 101 inserted into the radial through-hole 102a of an outer ring spacer 102 disposed on the side of the bearing 100 illustrated in FIG. 8B.
In this system, a lubricating component such as the nozzle piece 101 is separately required, which increases the number of parts of the spindle. This leads to an increase in the cost of the entire spindle and effort for management. Further, since the nozzle piece 101 is used, the shape of the outer ring spacer and the structure of the housing become complicated, and the labor of designing and machining of the spindle increases. Furthermore, since the nozzle piece 101 is installed on the axial side surface of the bearing, a certain length of the spacer length is required, and the axial length of the spindle is elongated. As a result, the size of the machine tool itself increases, the spindle weight becomes heavier as the length in the axial direction increases, and the whirling speed of the spindle (whirling speed is the rotational speed calculated from the natural frequency of the spindle, and turning the spindle in this whirling speed range results in large vibration) decreases. Also, due to the air curtain generated by high-speed rotation (air curtain is the wall of high-speed air flow in the circumferential direction generated by friction between air and the inner ring outer diameter surface rotating at high-speed), the supply of oil particles from the lubricating nozzle is hindered. As a result, lubricating oil may not be reliably supplied to the interior of the bearing and seizure may occur. In addition, since oil particles are supplied to the balls over the air curtain by the high-pressure air, there is also a problem that wind noise is generated when the high-pressure air collides with the balls. As described above, conventional oil-air lubrication has various problems due to its structure.
As another oil-air lubrication system, as illustrated in FIG. 9, there is known a system using an outer ring lubricating type bearing 110 having an oil groove 112 formed in the circumferential direction on the outer circumferential surface of the outer ring 111, and at the same axial position as the oil groove 112, an oil hole 113 formed to be directed in a radial direction (see, for example, Patent Document 1). In such an outer ring lubricating type bearing, even when the bearing is used at high-speed rotation, the supply of oil particles is not hindered by the air curtain. Therefore, it is possible to use a stable spindle even at high-speed rotation.
FIG. 10 is a schematic view of the spindle in the case of oil-air lubrication using the nozzle piece 101 and oil-air lubrication with the outer ring lubrication specification. The upper half of FIG. 10 is a spindle 120 for oil-air lubrication of the outer ring lubrication specification, and the lower half is the oil-air lubrication spindle 120A using the nozzle piece 101. In FIG. 10, reference numeral 121 denotes a rotary shaft, and reference numeral 122 denotes a rotor of a motor fitted to the rotary shaft 121. In this way, in the case of oil-air lubrication using the nozzle piece 101, in order to supply the lubricating oil from the side surface of the bearing 100, a spacer having a certain axial length or more is required. In contrast, in the case of the outer ring lubrication specification, since it is unnecessary to provide a lubricating spacer, it is possible to simplify the structure of the spacer and the reduction in size of the nozzle piece and to make the axial length of the spacer 123 shorter compared to the case of the specification using the nozzle piece. As a result, with the outer ring lubrication specification, it is easy to design and machine components for spindle and lubrication and manage the components, and overall cost reduction can be achieved in designing, manufacturing and managing of the machine tools. In addition, shortening the axial length of the spacer can lead to downsizing of the machine tool size and improving the spindle whirling speed.
Further, the bearing device using the outer ring lubricating type bearing 110 described in Patent Document 1 is described that the position in the circumferential direction between the lubricating oil introduction hole formed in the housing and the oil hole 113 of the outer ring 111 is made different, so that air passes through the oil groove 112 to lower the air flow velocity at the outlet of the oil hole 113, thereby reducing the noise value at high-speed rotation.